Sledování vážek malé tůně na Jižní Moravě
pomocí sběru exuvií
Emergence patterns of dragonflies from a small pool in South Moravia
(Czech Republic)
Michal STRAKA
Abstrakt
Ve sledované tůni byly po celou sezónu 2005 sbírány všechny svlečky líhnoucích se
vážek. Bylo nalezeno 10 druhů vážek a celková početnost přesáhla 2500 jedinců. Nebyly
prokázány odchylky od poměru pohlaví 1:1 ani asynchronní líhnutí samců a samic.
Jednotlivé druhy vyletovaly v pořadí: Coenagrion puella → Ischnura elegans, Lestes
barbarus → Lestes virens → Aeshna mixta, Sympetrum sanguineum → Sympetrum vulgatum, Sympecma fusca.
Introduction
Dragonflies (Odonata) are an insect group with great indicator abilities and as such
they are often used as bioindicators of the quality of aquatic systems (Dolný 2000,
Sahlen & Ekkestubbe 2001, Briers & Biggs 2003). Traditionally, data on dragonflies
were gathered by collecting or monitoring adults or, possibly, by studying larvae. Lately,
odonatologists have been more focused on collecting the exoskeletons of the last larval
instar – the exuviae. This progress in exuviae collecting began with the increasing ability to correctly identify larvae and with the publishing of good quality keys (for Europe
e.g. Carchini 1983, Askew 1988, Norling & Sahlén 1997, Gerken & Sternberg 1999,
Heidemann & Seidenbusch 2002). And even though the surveys based on adults still
predominate, there are some areas of dragonfly research where exuviae collecting is
irreplaceable, especially the mapping and management planning of rare species (Foster
& Soluk 2004), and exuviae collecting is also very important in autecological studies
(e.g. Ubukata 1984, Ferreras-Romero & Corbet 1995, Westermann 2002, Sonntag
2005, Hardensen 2008).
With the exuviae, it is possible to obtain crucial information about dragonfly emergence, which is considered as the most critical period in the life of dragonflies (Jakob
& Suhling 1999, Worthen 2010). The dragonfly exuviae can also be used as an additional tool for faunistic studies (e.g. Jakab et al. 2002, Kalkman et al. 2004, Dolný et al.
2007), and also when assessing habitat conditions (Chovanec & Raab 1997, D’Amico et
al. 2004, Aliberti Lubertazzi & Ginsberg 2010). The use of exuviae collecting to indicate habitat conditions is very undervalued in comparison to adult surveys, even though
it is known that the monitoring of adults can be strongly misleading when used to assess
the environmental quality of sites (Raebel et al. 2010). The main advantages of exuviae
collecting in comparison to the monitoring of adults are:
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Sborník referátů XIII. celostátního semináře odonatologů v Podyjí
▪ evidence that the given species really lives and reproduces at the site and is not an
allochthonous immigrant,
▪ the voucher specimen can be obtained without killing the dragonfly,
▪ the possibility of collecting in nearly all weather conditions and independently from
the daily activity patterns of adults,
▪ a good estimation of population density and sex ratio,
▪ a non-destructive method of obtaining material for population-genetics analysis
(Watts et al. 2005).
On the contrary, exuviae collecting is time consuming, in some cases the identification is doubtful and collecting is limited to easily accessible places.
The aim of the present study was: (i) to investigate species composition and the
abundance of dragonflies living in a small pool, (ii) to reveal the sex ratio during the
emergence period, and (iii) to compare the emergence patterns of the species found.
To fulfil these aims I decided to collect the exuviae of all species found throughout
the entire emergence period.
Study site and methods
A small pool, in which it was possible to go through and search as a whole in a relatively short period of time, was selected for the systematic collecting of exuviae. The
pool was located in what used to be a brick plant on the south-eastern edge of Hustopeče
(South Moravia, Czech Republic), at an altitude of approximately 200 m. a.s.l., and with
the following geographical coordinates: 48°55‘48“N, 16°44‘48“E. The surface of the
pool was 100 m2 in size and the average depth was 70 cm. Ninety percent of the pool’s
surface was covered with the common reed (Phragmites australis) and with broadleaf
(Typha spp.), whereas the remaining 10% (approximately) of the surface was free. The
location was regularly visited throughout the whole of the 2005 season, mostly at weekly intervals. The pool was thoroughly examined, and all of the sites of possible exuviae
emergence were searched. All the exuviae were collected and stored in 70% alcohol. In
the laboratory, the exuviae were identified according to Askew (1988), Carchini (1983)
and Gerken & Sternberg (1999). Based only on the exuviae, it was not possible to distinguish the following pairs of species: Coenagrion puella/pulchellum and Sympetrum
vulgatum/striolatum. However, since only adults of C. puella and S. vulgatum were
observed at the location, the following text will refer to them like that. For the species
which lay eggs endophytically (suborder Zygoptera, family Aeshnidae), sex was determined based on the presence/absence of an ovipositor (in cases where the back part of
abdomen of the exuvia was preserved).
Results
Ten species, from 2586 exuviae in total, were found at the locality (see Table 1).
The azure damselfly Coenagrion puella (Linnaeus, 1758) was the most numerous, for
which more than 1700 exuviae were found at this location, i.e. almost 70% of the total
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VÁŽKY 2010
number of dragonflies in the pool. The second most numerous was the common winter damselfly Sympecma fusca (Vander Linden, 1820) (302 exuviae), followed by the
ruddy darter Sympetrum sanguineum (Müller, 1764) (156 exuviae) and the blue-tailed
damselfly Ischnura elegans (Vander Linden, 1820) (144 exuviae). On the other hand,
the least numerous were large species, such as the emperor dragonfly Anax imperator
Leach, 1815 (two exuviae) and the broad-bodied chaser Libellula depressa Linnaeus,
1758 (one exuvia).
Table 1: A list of species and numbers of exuviae collected at the study location.
The total number, number of individuals of the given sex, and the period of time the exuviae
were found are given in the table.
N
♂
♀
Emergence lasts
(days)
Coenagrion puella
1771
837
843
51
Ischnura elegans
144
61
59
113
Lestes barbarus
64
28
34
58
Lestes virens
21
8
10
51
Sympecma fusca
302
144
141
77
Aeshna mixta
116
35
23
90
Anax imperator
2
2
0
1
Libellula depressa
1
1
Sympetrum sanguineum
156
126
Sympetrum vulgatum
67
62
Total
2586
1115
1110
164
Sex ratio
Even though it seemed that the sex ratio of some species was rather unbalanced (southern emerald damselfly Lestes barbarus (Fabricius, 1798) and migrant hawker Aeshna
mixta Latreille, 1805 – see Table 1), the chi-square test did not show any difference at
the 5% rejection level from the expected ratio of 1:1. In order to find out whether there
were any asynchronous emergences of individual sexes, the emergence curves were
created separately for males and females. These curves are shown in Figure 1. It was
impossible to observe one sex emerging before the other with any of the species found.
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Sborník referátů XIII. celostátního semináře odonatologů v Podyjí
Emergence patterns
Different emergence patterns were observed for different species (Figure 2).
Coenagrion puella turned out to be the species with the earliest emergence activity. The
first exuviae of this species were found as early as May 21st, and an overwhelming majority of this species emerged over the following two weeks. The first exuviae of I. elegans
were found together with the previous species; however, the period of emergence of this
species was a lot longer (113 days in total) and the largest number of exuviae was found
at the turn of June to July. At this point, the largest number of L. barbarus also emerged.
There was a similar emergence pattern for L. virens; in comparison with L. barbarus,
however, it emerged some two weeks later. The largest number of individuals of the
following four species emerged in the second half of August: S. fusca, A. mixta, S. sanguineum and Sympetrum vulgatum (Linnaeus, 1758). The longest emergence activity
was observed for S. vulgatum (126 days). However, it is necessary to bear in mind that
the exuviae of this species are easily mistakable for Sympetrum striolatum (Charpentier,
1840) which, theoretically, may live at this location, and so then two emergence curves
would be overlapping.
In general, it is possible to say that the dragonflies at this location in the season of
2005 emerged from the second half of May to the end of October in the following order:
C. puella → I. elegans, L. barbarus → L.virens → A. mixta, S. sanguineum → S. vulgatum, S. fusca.
Figure 1: Emergence curves for three selected species. Males are in grey (full line), females in
black (dotted line).
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VÁŽKY 2010
Figure 2: Lengths of time of the emergence of individual species. The whiskers mark the first
and last days of emergence, the boxes show 25–75% percentiles, and the middle point shows the
median points.
Discussion
The most abundant species was C. puella, which was not surprising because this
species is the most common dragonfly in the Czech Republic and often reaches high
abundances (Dolný et al. 2007). What was interesting was the high number of total
emerging individuals, because the data obtained by observing adult dragonflies can underestimate the population (pers. obs.). Also, the total number of exuviae found (2586)
underestimated the real number of emerged individuals due to losses caused by weather
conditions. Because the most frequent interval between the two collecting sessions was
seven days, it is necessary to add at least 40% to obtain the real number of emerged individuals (see Straka 2010). So the real number of all emerged dragonflies had probably
exceeded 3500 individuals in the pool with an area of 10 m × 10 m.
The sporadic findings of exuviae from A. imperator and L. depressa are consistent with the characteristics of the habitat. A densely vegetated pool is a typical habitat
of species of the Lestes-Sympetrum-Aeshna mixta coenosis (Dolný & Ašmera 1989),
where species A. imperator and L. depressa haven’t ecological optimum.
The theoretical model created by Crowley & Johansson (2002) implies that territorial species should have a female-dominant sex ratio upon emergence. In this study
(also in e.g. Baker et al. 1992, Stocks 2001) no difference from the expected ratio
of 1:1 was observed; however, no strongly territorial species was among the analysed
species. Also, Falck & Johansson 2000 observed an equal ratio between the sexes for
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Sborník referátů XIII. celostátního semináře odonatologů v Podyjí
S. sanguineum, but they found that the females emerged earlier than the males. In the
present study the emergence curves did not show any differences in the emergence patterns between the sexes.
The emergence patterns found for the different species were not unusual and, with
exception of Sympecma fusca, were in concordance with the known facts (e.g. Dolný et
al. 2007). According to Dolný et al. (2007), S. fusca shows its greatest emergence in the
second half of July. Also, Gerken & Sternberg (1999) and Heidemann & Seidenbusch
(2002) reported its emergence in Central Europe from July to August and Askew (1988)
reported its emergence from the end of July to early September. In the light of these
facts, the main emergence of S. fusca found in the present study at end of August and
the beginning of September was rather unusual, and the last exuviae of this species were
collected on 22.10.2005: this finding shifted the known emergence period to about one
month later than previously reported (Dolný et al. 2007). Unfortunately, in a one-year
study it was impossible to determine the reason for this unusual emergence pattern of S.
fusca, which may be caused by some stochastic reason e.g. colonization history.
Acknowledgements
This paper was supported by the long-term research plan MSM 0021622416. I wish
to thank my wife Petra and Jiří Nečas for their assistance in the field.
Literature cited
Aliberti Lubertazzi M. A. & Ginsberg H.
S. 2010: Emerging dragonfly diversity
at small Rhode Island (U.S.A.) wetlands
along an urbanization gradient. Urban
Ecosystems 13(4): 517 – 533.
Askew R. R. 1988: The Dragoflies of
Europe. Harley Books, Colchester.
Baker R. L., Forbes M. R. L. & Proctor
H. C. 1992: Sexual differences
in development and behaviour of
larval Ischnura verticalis (Odonata:
Coenagrionidae). Can. J. Zool. 70(6):
1161 – 1165.
Briers R. A. & Biggs J. 2003: Indicator
taxa for the conservation of pond
invertebrate
diversity.
Aquatic
Conservation
–
Marine and
Freshwater Ecosystems 13: 323 – 330.
Carchini G. 1983: A key to the
Italian Odonata larvae. Societas
Internationalis Odonatologica Raid
Communicatios (Supplements) 1,
Utrecht.
Chovanec A. & Raab R. 1997: Dragonflies
(Insecta, Odonata) and the ecological
status of newly created wetlands:
Examples for long-term bioindication
programmes. Limnologica 27: 381 –
392.
Crowley P. H. & Johansson F. 2002:
Sexual dimorphism in Odonata: age,
size, and sex ratio at emergence. Oikos
96: 364 – 378.
D’Amico F., Darblade S., Avignon
S., Blanc-Manel S. & Ormerod
S. J. 2004: Odonates as Indicators
of Shallow Lake Restoration by
Liming: Comparing Adult and Larval
Responses. Restor. Ecol. 12(3): 439 –
446.
77
VÁŽKY 2010
Dolný A. 2000: Vážky (Odonata) jako
biologické indikátory. p. 8 – 23. In:
Hanel L. (ed.) Vážky 2000 (sborník
referátů z celostátního semináře).
ČSOP Vlašim.
Dolný A. & Ašmera J. 1989: Příspěvek
k ekologickému hodnocení vážek.
Studia oecologica 2: 9 – 15.
Dolný A., Bárta D., Waldhauser M.,
Holuša O., Hanel L. et al. 2007:
Vážky České republiky: Ekologie,
ochrana a rozšíření / The Dragonflies
of the Czech Republic: Ecology,
Conservation
and
Distribution.
Vlašim: Český svaz ochránců přírody
Vlašim, 672 pp.
Falck J. & Johansson F. 2000: Patterns in
Size, Sex Ratio and Time at Emergence
in a South Swedish Population of
Sympetrum sanguineum (Odonata).
Aquatic Insects 22 (4): 311 – 317.
Ferreras-Romero M. & Corbet P. S.
1995: Seasonal Patterns of Emergence
in Odonata of a Permanent Stream in
Southwestern Europe. Aquatic Insects
17(2): 123 – 127.
Foster S. E. & Soluk D. A. 2004:
Evaluating exuvia collection as
a management tool for the federally
endangered Hine’s emerald dragonfly,
Somatochlora hineana Williamson
(Odonata: Cordulidae). Biological
Conversation 118: 15 – 20.
Gerken B. & Sternberg K. 1999:
Die Exuvien Europäischer Libellen
(Insecta, Odonata). Arnika & Eisvogel
Höxter und Jena.
Hardensen S. 2008: Dragonfly (Odonata)
communities at three lotic sites with
different hydrological characteristics.
Italian Journal of Zoology 75(3): 271
– 283.
78
Heidemann H. & Seidenbusch R. 2002:
Die Libellenlarven Deutschlands.
Handbuch
für
Exuviensammler.
Goecke & Evers, Keltern.
Jakab T., Müller Z., Dévai G.Y. &
Tóthmérész B. 2002: Dragonfly
assamblages of a shallow lake type
reservoir (Tisza-tó, Hungary) and
its surroundings. Acta Zoologica
Academiae Scientiarum Hungaricae
48(3): 161 – 171.
Jakob Ch. & Suhling F. 1999: Risky
Times? Mortality During Emergence in
Two Species of Dragonflies (Odonata:
Gomphidae, Libellulidae). Aquatic
insects 21(1): 1 – 10.
Kalkman V., Kop A., van Pelt G. J. &
Wasscher M. 2004: The dragonflies of
Summary
All the exuviae of emerging dragonflies were regularly collected from
the studied pool throughout the entire
emergence period in 2005. Ten species of dragonflies were found with the
total number exceeding 2500 individuals. Neither deviations from the sex
ratio of 1:1 nor asynchronous emergences of females and males were
proven. The individual species emerged from the second half of May until
the end of October in the following
order: Coenagrion puella → Ischnura
elegans, Lestes barbarus → Lestes
virens → Aeshna mixta, Sympetrum
sanguineum → Sympetrum vulgatum,
Sympecma fusca.
Keywords
exuviae, emergence, dragonflies,
Odonata, phenology, sex ratio
Sborník referátů XIII. celostátního semináře odonatologů v Podyjí
the surroundings of lake Köyceğizand
the river Eşen, Muğla province,
SW Turkey (Odonata). Libellula
supplement 5: 39 – 63.
Norling U. & Sahlén G. 1997: Odonata,
Dragonflies and Damselflies. In:
Nilsson A. N. (ed.): Aquatic Insects of
North Europe – A Taxonomic Handbook
(2). Apollo Books, Stenstrup.
Autor
Michal Straka
Institute of Botany and Zoology,
Faculty of Science,
Masaryk University,
Kotlářská 2, 611 37 Brno,
Czech Republic
michal.straka@centrum.cz
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